This proposal is based on the hypotheses that cells lining the surface of the tooth root, cementoblasts, responsible for producing cementum, are positional osteoblasts. These cells exhibit an "osteoblast-like" phenotype distinct from odontoblasts, despite their common dental ectomesenchymal origin. The rationale for these hypotheses include our findings that bone sialoprotein (BSP), a mineralized tissue specific protein, is expressed by cells along the root surface and localized to cementum coinciding with initiation of cementogenesis. To test our hypotheses, we propose to; 1) establish cementoblast cultures and investigate their phenotypic characteristics and mechanism of action. For this aim, primary and immortalized cementoblast cultures will be established and characterized from developing first mandibular molars in mice. 2) identify specific differences in gene expression between cementoblasts and odontoblasts using mRNA differential display. Genes that are expressed uniquely by either cell type will be isolated and characterized. The establishment and characterization of cementoblast populations will enhance our knowledge of cementogenesis and basic mineralized tissue biology, thereby providing information required to develop therapies for regeneration of tissues lost as a consequence of periodontal disease.